1. Field of the Invention
The present invention relates to an arrangement for the thermoforming of molded plastic articles from a continuous web of a thermoplastic material, and more particularly, relates to a trim in place thermoforming arrangement in which the plastic articles are simultaneously molded and at least substantially or completely separated from the remaining thermoplastic web material.
The continually increasing demands on industry and commerce for supplying consumers with numerous kinds of molded plastic articles for the most divergent uses, such as plastic dishes, cups, utensils and various types of containers, has generated a requirement for the development of more efficiently operating equipment which will afford the rapid and inexpensive thermoforming or molding of such articles from a continuously or intermittently advanced continuous web or sheet of a thermoplastic material. In many instances, the articles are thermoformed or molded in a first forming station through the utilization of mutually cooperating male and female molding dies, and thereafter the entire thermoplastic sheet material together with the molded plastic articles, conveyed to a separate trimming station in which the molded articles are separated from the remaining sheet material by a trimming procedure implemented through the employment of suitable trimming cutters or blades.
In order to improve upon the foregoing, apparatus has been developed in this technology, in which the thermoformed or molded plastic articles are at least substantially, and even completely separated from the thermoplastic sheet material while the molded articles are still in the thermoforming or molding station of the apparatus. This procedure eliminates the necessity for the provision of separate apparatus for trimming the articles from the thermoplastic sheet material at a different location from the molding station, and is commonly referred to in the technology as a trim in place molding or thermoforming operation.
Among the different types of thermoforming apparatus which are currently employed for the trim in place operation of cutting or separating the thermoformed or molded articles from the remaining thermoplastic sheet material, in essence, the scrap material remainder, are those which completely separate the molded plastic article from the sheet material, thereby necessitating the separate step of removing the separated articles from the interspace between the cooperating molding die members while advancing the remaining sheet material. Alternatively, other types of trim in place molding apparatus contemplate the material articles being only substantially separated from the remaining sheet material so as to adhere thereto at one or more locations whereby the entire web of sheet material inclusive of the molded articles are advanced out of the trim in place thermoforming station of the apparatus, and the articles are then subsequently separated either manually or automatically from the remaining thermoplastic sheet material.
Although the methods of employing such apparatus for the trimming in place of the molded articles from the remaining thermoplastic sheet material have proven themselves to be generally satisfactory in use, the cutting devices which are employed for the trim in place operation are subjected to extensive wear during the continual and repetitive utilization thereof, as a consequence of thermal stresses and misalignments and the like, thereby frequently rendering current types of such apparatus uneconomical.
Generally, such trim in place thermoforming devices or apparatus employ mutally cooperating interengageable cutting blade members, which are attached to, respectively the male and female molding die members, and which circumferentially encompass the molded plastic article which is to be cut or separated out of the thermoplastic sheet material, and possess an article-trimming configuration substantially in conformance with the peripheral dimensions of the article. Hereby, during the thermoforming sequence effecting the molding of the articles, the cutting blade members have cutting edges come into sliding or shearing surface contact so as to essentially shear the molded article from the sheet material. Such shearing surfaces on the cutting blade members are generally required to be within close tolerances and in perfect alignment during operation and are subject to the need for implementing a secondary mold action to allow for the sliding or shearing interaction of the blade cutting surfaces. The undue amount of wear normally encountered by cutting blades which are employed in trim in place operations, frequently necessitates their replacement by other blades, and the refinishing or regrinding of the cooperating cutting blade surfaces thereby increasing the cost of operation because of the necessity for extensive periods of downtime of the entire apparatus for the replacement of the trim in place cutting blades, and the additional expenditures necessitated by the refinishing of the worn blades.
Furthermore, according to presently employed trim in place thermoforming apparatus and tools, the fact that the trimming or cutting blades are frequently subjected to undue amounts of wear, frequently produces either an uneven or incomplete cut through the plastic material extending about the periphery of the plastic molded article, so as to either leave rough and unfinished-looking or unsightly rims or edges extending about the article, or alternatively, incompletely cuts through the sheet material at various locations so as to render difficult the separation of the molded article from the remainder of the thermoplastic sheet material.
2. Discussion of the Prior Art
Among various prior art trim in place thermoforming apparatuses of the type under consideration herein, some are of particular significance.
Jope, et al. U.S. Pat. No. 3,640,666 discloses a trim in place thermoforming apparatus in which a continuous sheet of a thermoplastic film material is advanced between sets of mutually cooperating or complementary male and female molding die members which are adapted to be reciprocated towards and away from each other so as to effect the thermoforming of molded articles in the film material during a closing stroke between the molding dies. Concurrently with the thermoforming sequence, a pair of cooperating blade members mounted on the respective die members compress the film material about the periphery of each molded article so as to allow for the ready separation of each molded article from the remaining sheet material in the absence of any rough or unsightly peripherally extending rims or edges on the articles. Although the disclosed structure is designated as a socalled trim in place thermoforming apparatus, the trimming blades do not actually cut through the material so as to separate the molded article from the sheet material, but rather is designed to merely produce a compression of the thermoplastic material about the circumference of the molded article to facilitate it to be bent downwardly and thereafter manually separated from the sheet material. There is no provision of a sharp cutting or shearing action provided by the trim in place separation of molded articles in a manner analogous to that of the present invention, and wherein a cutting blade support structure is provided to always maintain the cutting or trimming blade components in a substantially aligned and relative low-wear position with respect to each other; thereby affording an enhanced degree of accuracy and precision in trimming the molded article from the sheet material, while concurrently maintaining the wear on the components of the trim in place cutting blade structure to an absolute minimum.
Dulmage U.S. Pat. No. 2,270,187 discloses a machine for drawing plastic articles from a flat thermoplastic plate or sheet material, and concurrently trimming the article, by means of an annularly extending cutter, from the remaining sheet material, so as to thereby carry out a simultaneous drawing and trimming operation. The annular trimming blade of the cutter employed in this patent requires the maintaining of an extreme close degree of precision or tolerance relative to a stationary encompassing ring, and is subject to a considerable amount of wear which will adversely effect the long-term or continual operation of the apparatus.
Knowles U.S. Pat. No. 3,470,281 relates to a method for forming a flanged container or the like, in which a shearing unit is employed for the subsequent trimming of a molded plastic article from a plastic sheet material. This is not in any manner analogous to the trim in place arrangement pursuant to the present invention.
Griese U.S. Pat. No. 3,368,440 discloses an anvil-type shearing machine for removing articles from sections of a plastic material, but is not analogous to the inventive trim in place thermoforming arrangement.
Roberg, et al. U.S. Pat. No. 4,095,927 discloses a thermoforming apparatus for forming molded articles which also incorporates a trimming device possessing blades which are laterally fixed relative to the molding unit. This type of trimming operation also requires extreme precision and close tolerances for the cutting unit while concurrently imparting a high degree of wear to the cutting blades.
Meadors U.S. Pat. No. 4,127,378 discloses a cold-forming apparatus for thermoplastic sheeting, in which the edge of a molded article is adapted to be heated and thereafter trimmed. This disclosure does not provide for the unique trim in place structure pursuant to the present invention.
Although numerous other types of apparatus, devices and methods are currently in use with regard to the trimming of thermoplastic articles which are molded or thermoformed into a web of a thermoplastic sheet material, none of these disclose a trim in place arrangement similar to that provided for by the present invention.